The subject matter disclosed herein relates generally to touchscreens and touchscreen systems, and more particularly to projected capacitive touchscreens.
In a projected capacitive touchscreen, an outer surface may be provided over one or more layers having sense electrodes or sensors formed thereon. In contrast to common resistive touchscreens, the outer surface of a projected capacitive touchscreen may be a durable glass surface having high optical transparency for viewing images displayed by an underlying display device. The touchscreen may be positioned over a display device that displays graphical selections such as buttons and icons. When a user touches the outer surface with a finger, corresponding to a desired selection displayed on the display device, the touchscreen system senses a change in capacitance associated with one or more of the electrodes. “Projected capacitive” touchscreen is in contrast to a “surface capacitive” touchscreen that has a single sensing electrode covering the entire touch area. As used herein, “projected capacitive touchscreen” generalizes to any capacitive touchscreen with a plurality of sensing electrodes in the touch sensitive area.
Some projected capacitive touchscreens use a “backgammon” type of configuration for the electrodes. In this configuration, the electrodes are elongated triangles formed on a single surface. The orientation of adjacent electrodes alternates, wherein a base of a first electrode is positioned proximate one edge of the surface and the base of the next or adjacent electrode is positioned proximate the opposite edge of the surface. Such electrode geometry is reminiscent of a backgammon game board pattern. Such designs have the cost advantage of providing two-dimensional touch coordinates with a single plane of sense electrodes.
Backgammon touchscreen designs typically have a large number of narrow electrodes so that each touch is detected by at least two electrodes. For example, in some backgammon systems the electrodes detect signals that are used to determine both the X and Y coordinates. If each touch is detected by a very large number of electrodes, a fraction of the total signal on the electrodes that are oriented the same way provides an accurate measure of one of the coordinates, such as the Y or vertical coordinate. However, typically each touch is detected by a more modest number of electrodes and as a result the fraction of the total signal on the electrodes that are oriented in the same way may not provide an accurate and reliable coordinate measurement. There is a need for improved coordinate determinations based on touch induced electrode signals.